The levitation of a magnet above a superconductor has been demonstrated, particularly with regard to high temperature superconductors. When the magnet is levitated above the superconducting plane, the superconductor operates to exclude the magnet's field in accordance with the Meissner effect. Eddy currents occur in the superconductor such that a mirror image effect is produced and the magnet is repelled. This phenomenon is demonstrated in FIG. 1 where a magnet 1 is levitated above a superconducting plane 2.
The magnitude of the flowing current (I) in the superconducting plane is limited by the critical current of the superconducting material employed to fabricate the superconducting plane 2. In FIG. 1 the height at which the magnet 1 is levitated above the superconducting plane 2 is not controlled, and assumes an equilibrium position.
The following chronologically ordered U.S. Patents and journal articles are referenced as describing various aspects of superconductor-induced levitation and related issues.
In U.S. Pat. No. 3,327,265, issued Jun. 20, 1967, entitled "Superconductive Device for Causing Stable and Free Floating of a Magnet in Space", van Geuns et al. describe a suspension system that suspends a permanent bar magnet over a plate of superconductive material. The plate includes apertures 3 and 4 that locally eliminate a mirror-image effect for attenuating the induced magnetic field near the poles of the magnet.
In U.S. Pat. No. 3,951,074, issued Apr. 20, 1976, entitled "Secondary Lift for Magnetically Levitated Vehicles", Cooper discloses an arrangement of magnets for providing a secondary lift effect for a magnetically levitated vehicle.
In U.S. Pat. No. 4,797,386, issued Jan. 10, 1989, entitled "Superconductor-Magnet Induced Separation", Gyorgy et al. describe superconductivity-magnetic induced separation in which a need for geometry and/or ancillary elements for lateral stabilization are said to be avoided. Superconducting elements are made of Type II superconductors such as barium-yttrium copper oxide. A magnet is levitated over a superconducting support body and induces vortices 5 and 6 for laterally stabilizing the magnet.
In an article entitled "Levitation of a Magnet over a Flat Type II Superconductor", Journal of Applied Physics, Vol. 63, pages 447-450 (Jan. 15, 1988) F. Hellman et al. disclose the levitation of a magnet over a Type II superconductor in a manner similar to that described in the immediately preceding U.S. Patent.
In U.S. Pat. No. 4,843,504, issued Jun. 27, 1989, entitled "Superconductor Devices Useful for Disk Drives and the Like", Barnes describes superconducting materials for use in magnetic recording devices. Superconducting Josephson junction devices are shown to be used for detecting magnetic field changes.
In U.S. Pat. No. 4,879,537, issued Nov. 7, 1989, entitled "Magnetic Suspension and Magnetic Field Concentration Using Superconductors", Marshall et al. describe a device for suspending a load by the use of a magnetic field and superconductive material. A magnetic is suspended over a superconductor so as to provide a magnetic field that penetrates the superconductor. A superconducting disk is comprised of a Type II superconductor comprised of YBa.sub.2 Cu.sub.3 O.sub.x and the magnet is comprised of Neodymium-Iron-Boron. In col. 3, a discussion is made of levitation forces for a Type II superconductor, as described by F. Hellman et al. in the above referenced Journal of Applied Physics article.
In U.S. Pat. No. 4,892,863, issued Jan. 9, 1990, entitled "Electric Machinery Employing a Superconductor Element" Agarwala describe a superconductor bearing comprised of Type I or Type II superconducting material.
In an article entitled "Observation of Enhanced Properties in Samples of Silver Oxide Doped YBa.sub.2 Cu.sub.3 O.sub.x " Applied Physics Letters, Vol. 52, pages 2066-2067 (Jun. 13, 1988), P. N. Peters et al. describe the addition of silver oxide to YBa.sub.2 Cu.sub.3 O.sub.x to provide a material that exhibits attractive forces in gradient magnetic fields, both normal and tangential to the surfaces, which are more than twice the sample weight. This is shown to enable the suspension of a sample of this material below a rare earth magnet.
In an article entitled "Magnetic Hysteresis of High-Temperature YBa.sub.2 Cu.sub.3 O.sub.x AgO Superconductors: Explanation of Magnetic Suspension", Modern Physics Letters B, Vol. 2, pages 869-874 (August, 1988) C. Y. Huang et al. discuss in greater detail the characteristics of the silver oxide doped YBa.sub.2 Cu.sub.3 O.sub.x superconductor described in the immediately preceding article. The presence of extremely strong pinning centers in the superconductor is discussed.
In an article entitled "Levitation Effects Involving High T.sub.c Thallium Based Superconductors" Applied Physics Letters, Vol. 53, pages 1119-1121 (Sep. 19, 1988) Harter et al. describe a stabile levitation equilibria exhibited by the superconductor Tl.sub.2 Ca.sub.2 Ba.sub.2 Cu.sub.3 O.sub.10.
In an article entitled "Friction in Levitated Superconductors" Applied Physics Letters, Vol. 53, pages 1554-1556 (Oct. 17, 1988) E. H. Brandt describes the levitation of Type I and Type II superconductors above a magnet. The author points out that, in contrast to Type I superconductors, levitated Type II superconductors with flux pinning exhibit a continuous range of stable positions and orientations.
In an article entitled "Magnetic Suspension of Superconductors at 4.2K" Applied Physics Letters, Vol. 53, pages 2346-2347 (Dec. 5, 1988) R. Adler et al. describe suspension at low temperature for a Type II superconductor such as Nb.sub.3 Sn.
And, in an article entitled "Flux Penetration in High-T.sub.c Superconductors: Implications for Magnetic Suspension and Shielding" Applied Physics, Vol. A48, pages 87-91 (January, 1989) D. Marshall et al. describe two phenomena which result from flux penetration and pinning in a superconductor. These phenomena include magnetic suspension, wherein a magnet is suspended stably beneath another magnet with a superconductor interposed between the two magnets, and the intensification of magnetic flux upon passing through a superconductor.
What is not taught by this prior art, and what is thus an object of the invention to provide, is the active control of the levitation of a magnetic body relative to a superconductor.
A further object of the invention is to provide a superconducting structure comprised of Josephson junction devices that enable the controlled levitation and positioning of a magnetic body relative to the superconducting plane.
Another object of the invention is to provide a superconducting plane that includes a plurality of electrically addressable devices to enable the precise control of levitation height and a position of a magnetic body above a superconductor.